QImage::scaled crashes on images with big width due to internal integer overflow

When scaling images with big width, e.g. (60000x1), there is a crash internally in Qt.
When no crash happens part of the scaled image is corrupted.

This is a simple code snippet to reproduce the problem

QImage img(QSize(60000, 1), QImage::Format_RGB32);
img.fill(Qt::black);
QImage imgScaled = img.scaled(QSize(600, 1), Qt::KeepAspectRatio);
imgScaled.save("a.bmp");

The crash is due to an integer overflow happening both in internal functions qt_scale_image_16bit and qt_scale_image_32bit (implemented in src/gui/painting/qblendfunctions_p.h) in internal loop when srcx counter is increased.

The problem affects latest Qt 4 and Qt 5 versions (Qt 5.3.1 and Qt 4.8.6) on all platforms I tested (Windows, Mac, Linux)